Magnetic discs with magnetizable media are used for data storage in most all computer systems. Current magnetic hard disc drives operate with the read-write heads only a few nanometers above the disc surface and at rather high speeds, typically a few meters per second. Because the read-write heads can contact the disc surface during operation, a layer of lubricant is coated on the disc surface to reduce wear and friction.
FIG. 1 shows a disk recording medium and a cross section of a disc showing the difference between longitudinal and perpendicular recording. Even though FIG. 1 shows one side of the non-magnetic disk, magnetic recording layers are sputter deposited on both sides of the non-magnetic aluminum substrate of FIG. 1. Also, even though FIG. 1 shows an aluminum substrate, other embodiments include a substrate made of glass, glass-ceramic, NiP/aluminum, metal alloys, plastic/polymer material, ceramic, glass-polymer, composite materials or other non-magnetic materials.
Generally, the lubricant is applied to the disc surface by dipping the disc in a bath containing the lubricant. The bath typically contains the lubricant and a coating solvent to improve the coating characteristics of the lubricant, which is usually viscous oil. The discs are removed from the bath, and the solvent is allowed to evaporate, leaving a layer of lubricant on the disc surface.
The lubricant film on hard discs provides protection to the underlying magnetic alloy by preventing wear of the carbon overcoat. In addition, it works in combination with the overcoat to provide protection against corrosion of the underlying magnetic alloy. Reliability of hard disks is depends on the durability of the thin film media. As the spacing between head disk is being reduced aggressively to improve area storage density, media are facing many severe technical obstacles, such as weak durability, heavy lubricant pickup, unmanageable stiction/friction, etc. Lubrication plays unquestionably an important role in overcoming these technical difficulties.
Because the thickness of the carbon overcoat and lubricant protective layers is being reduced continuously, a more integrated protection structure is needed. Lubrication additive moieties, such as Bis(4-fluorophenoxy)-tetrakis(3-trifluoromethyl phenoxy) cyclotriphosphazene (X1-p) can improve tribological performance and corrosion resistance of thin film media. Dip-lubrication is a process which includes immersing disks into a solution containing both lubricant moieties and additive moieties, and then slowly removing disks from the lubricant solution, or alternatively, slowly draining the solution away from the disks. The amount of lubricant moieties and additive moieties adsorbed on the disk overcoat is controlled by varying the solution concentration and the drain rate. However, the X1-p moiety is sparingly soluble in the perfluoropolyether (PFPE) lubricant moieties, resulting in a two-phase lubricant moiety/additive moiety system. The use of such a two-phrase system can lead to phrase separation of the additive moieties on the disk, resulting in flyability issues with read-write head. To eliminate these performance problems, lubricant moieties (such as Zdol, defined below) can be linked directly to a cyclotriphosphazene moiety by a chemical synthetic method. However, typical chemical synthesis process to couple cyclotriphosphazene moiety with a lubricant moiety involves multiple-step chemical reactions. In addition, complicated and time-consuming purification is required afterward. Yield of the multiple-step reactions is also undesirable low.